Ms. Clifford, who received $130,000 from Mr. Cohen weeks before the election, has sued him, seeking to be released from that agreement, which her lawyer has argued is invalid because Mr. Trump did not sign the contract.
Ms. McDougal similarly sued American Media Inc., the media company that had paid her $150,000 for the rights to her story, arguing that she was deceived into accepting the terms. She said that Mr. Davidson, acting as her own lawyer, inappropriately pressured her and secretly colluded with Mr. Cohen, who was not technically part of the negotiation. This week, A.M.I., the parent company of The National Enquirer, freed her from that agreement.
Yet another former Playboy model was represented by Mr. Davidson in recent months, as he negotiated another agreement with Mr. Cohen. Under that contract, Elliott Broidy, the deputy finance chairman of the Republican National Committee, agreed late last year to pay $1.6 million to the woman, who had become pregnant during an affair with Mr. Broidy. Mr. Broidy resigned last week after reports of the agreement emerged.
Like Ms. Clifford and Ms. McDougal, the woman who settled with Mr. Broidy has sought a new lawyer and is no longer represented by Mr. Davidson.
Mr. Davidson’s past client list has included the professional athletes Jalen Rose and Manny Pacquiao, as well as gossip-page regulars who placed him in the middle of the sex-tape cases of the “Austin Powers” actor Verne Troyer, the wrestler Hulk Hogan and the onetime Playboy model and MTV host Tila Tequila.
Mr. Davidson has called Mr. Cohen a friend, and this month he defended his professional integrity to CNN and said that Mr. Cohen had encouraged him to talk to the media and “spill my guts.”
The investigators who have sought information from him are working separately from the special counsel Robert S. Mueller III, though the special counsel’s office referred certain information to them.
Among the evidence that the authorities in New York have seized are recordings of conversations that Mr. Cohen secretly made. Mr. Davidson, who works out of two offices in Southern California, would need to have agreed to Mr. Cohen recording any phone calls they may have had, as California law requires that both people involved in a conversation consent.